The conversion of diesel engines into natural gas operation has been an aspiration of the internal combustion engine industry for a period of time. Natural gas is a clean burning fuel (relative to diesel) with improved emission levels of both nitrogen oxides (NOx) and particulate matter. Thus, increasing concern over exhaust emissions regulation and fuel efficiency have led to an interest in burning a combustible gaseous mixture, such as propane or natural gas in diesel engines, particularly in diesel engines used in road HD trucks, stationary, marine, and locomotive applications. Thus, a method of converting diesel engines to spark ignited engines that will meet Environmental Protection Agency (“EPA”) and California Air Resources Board (“CARB”) ultra low emission standards is desired.
A number of strategies have been used for the conversion of diesel engines to spark ignited natural gas engines. Such conversions have included replacing the diesel fuel injectors with spark plugs connected to a suitable ignition system and providing a throttle body on the intake manifold. See Friddell, U.S. Pat. No. Re. 26,145. Another method involves changing the camshaft lobes to change intake and exhaust opening timings so that the compression ratio does not need to be changed. See Chen, U.S. Pat. No. 5,315,981. Another conversion method involves utilizing a rocker and fulcrum mechanism to open the exhaust valves of the engine to degrease the reflux of exhaust gasses into the combustion chamber. See Bennett, U.S. Pat. No. 4,911,124. However, none of these methods has been fully satisfactory in the conversion process.